The Armor of Gloom is a very interesting item. It has the highest possible Armor Class, but is penalized by 0% resistance to all. This would be the ultimate armor for a melee character on a level without witches or mages, but the bug in the item generation mechanism makes it virtually nonexistent. It can only be found in single player mode, if the unique Demon Plate has already been found in the same game.
Armor of Gloom
Full Plate Mail